1. Field of the Invention
This invention relates to a refrigeration system having a thermodynamic refrigeration cycle characteristic, and more particularly, but not by way of limitation, to a refrigeration system of the type for use in a car cooler and a domestic electric refrigerator.
2. Description of Prior Art
In a conventional refrigeration system, as illustrated in FIG. 1, a gaseous refrigerant is compressed by a compressor 1 so as to have a high temperature and a high pressure and fed to a condenser 2, where the gas is air-cooled or water-cooled so as to be condensed and liquefied. The so liquefied refrigerant has an ordinary temperature and a high pressure and is fed to an expansion valve 3 where the refrigerant is subjected to pressure reduction so that the temperature and pressure thereof are lowered and a portion of the refrigerant is gasified. Therefore, the refrigerant introduced into an evaporator 4 is a mixture of gaseous and liquid refrigerant. The mixing ratio is expressed in terms of dryness x and wetness 1-x according to a Mollier diagram. The refrigerant introduced into the evaporator 4 receives a heat load from the outside so that the liquid portion thereof is also gasified and recycled to the compressor 1. In this connection, it is to be noted that the liquid portion of the refrigerant effects a large work relative to the outside by the latent heat thereof, but the gaseous portion of the refrigerant can effect only a little work corresponding to a heat-sensing change. The work done is expressed in terms of a difference in enthalpy. For instance, the enthalpy difference by evaporation at 0.degree. C. is 36.180 kcal/kg, while the enthalpy difference is 1.005 kcal/kg when a gas of 0.degree. C. is overheated by 10.degree. C. Thus, it is apparent that there is a significant difference between works done by liquid and gas. In this respect, it is further to be noted that the gaseous portion of the refrigerant fed from the expansion valve 3 to the evaporator 4 does little work and yet it lowers a heat conductivity (the heat conductivity of liquid is 8.8 times as large as that of gas) and increase a rate of flow (the specific volume of liquid is 13 times as large as that of gas) to lower a heat transmission coefficient. A passage 5 led from the expansion valve 3 to the evaporator 4 illustrated in FIG. 1 is, as known, to measure a temperature at an outlet of the evaporator for controlling a flow of the refrigerant to the expansion valve 3. In the system of FIG. 1, the expansion valve employed is of an internal pressure equalization type.
FIG. 2 illustrates another conventional system, wherein an external pressure equalization type expansion valve 3' is employed. In this case, a passage 6 for measuring a pressure at the outlet of the evaporator 4 is provided as well as a passage 5 for measuring a temperature at the outlet of the evaporator 4. The passage 6 is also led from the expansion valve 3' to the evaporator 4. A flow of the refrigerant to the expansion valve 3' is controlled by the temperature and pressure measured through the passages 5 and 6, respectively. The circulation route of the refrigeration in the system of FIG. 2 is indentical with that in the system of FIG. 1, so that the system of FIG. 2 involves similar problem to that of FIG. 1.